The Procyon System is located about
11.5 light-years (ly) from our Sun, Sol -- slightly higher than
HIPPARCOS' estimate of 11.4 ly
(Girard
et al, 2000). Procyon A, or Alpha Canis
Minoris A, is the brightest and most centrally located naked-eye star
(07:39:18.12+05:13:29.98, ICRS 2000.0) of Constellation
Canis
Minor (the Smaller Dog). Procyon is also the upper left member of the
"Winter
Triangle" of first magnitude stars, whose other components are
Sirius (Alpha Canis Minoris) at lower left and
Betelgeuse (Alpha Orionis) at
right center (see also wide-field image from
Astronomy
Picture of the Day).

Alpha Canis Minoris A has a close companion star B that is separated
"on average" by only about 16 times the distance from the Earth to the
Sun -- 14.9 astronomical units (AUs) of an orbital semi-major axis --
which is roughly the distance between Uranus
and our Sun. Alpha Minoris B, the companion star, is a white dwarf,
stellar remnant and is so dim that it cannot be perceived with the
naked eye. After analyzing irregularities in the proper motion of
Procyon which were first detected in 1840,
Arthur
Julius Georg Friedrich von Auswers (1838-1915) deduced the presence
of this faint but massive companion and published a computed period of
40 years in 1861. However, Procyon B was not detected visually until
1896 by
John
Martin Schaeberle (1853-1924) with the 36-inch refractor at
Lick Observatory. There
is a third optical companion C.

Procyon A appears to be a relatively young star with only around
1.8 billion years
(Leccia
et al, 2007;
Kenneth Croswell,
2005; and
Eggenburger
et al, 2005). However, being so much bigger and hotter Sol,
the star will exhaust its core hydrogen within even the 4.6 billion
years of Sol's current age and turn into a red giant before puffing
away its outer layers to reveal a remnant core as a white dwarf.
Indeed, Procyon A is unusually bright for its spectral type and so
may be becoming a subgiant star that is beginning to evolve off the
main sequence, as it begins to fuse the increasing amounts of helium
"ash" mixed with hydrogen at its core. Analysis of "soft x-ray"
emissions from Silicon ions indicate that Procyon's coronae is
cooler than Sol's
(Liang
and Zhao, 2008).

Many astronomers believe that the star has entered the last phase
of its life and is becoming dimmer. As a result of studies conducted
on the oscillation of our Sun, Sol, Procyon A should be oscillating
in a certain pattern. When the
Canadian Space Agency's
MOST satellite
monitored Procyon A for 32 consecutive days from January to February
2004 and in 2005, no oscillations were detected although the aging
star should have vibrated and oscillated at a greater amplitude than
Sol. As a result, models based on observations of Sol, for measuring
stellar (p-mode) oscillations due to "turbulent convection" of its
outer layers are being reexamined (UBC
press
release; and
Guenther
et al, 2007). In 2008, its oscillations were measured
and found to have "a plateau of excess power ... [that] is
broader than has been seen for other stars", and there is
also "a slow variation in the radial velocity of Procyon ...
[which] are remarkably similar to those seen in the Sun, and
we interpret them as being due to rotational modulation from
active regions on the stellar surface ... [with] a period of
about 10 days"
(Arentoft
et al, 2008).

The star is rich in elements heavier than hydrogen ("metals rich"), as
it has about 1.4 times the iron abundance of Sol, and dust has been
detected in the system
(Kuchner
and Brown, 2000 -- in
postscript).
It was probably
enriched by its companion star, which was once bigger and hotter than
Procyon A and so evolved and "burnt out" even faster. Procyon B
manufactured lots of heavier elements which it puffed out into space
and onto Procyon A before becoming a white dwarf.

Procyon A is a
BY
Draconis-type variable star. Not only can its companion
boost its brightness when located in front of the star as
observed from Earth, but its intrinsic brightness actually
varies as well. In addition to its New Suspect Variable (NVS)
designation of NVS 3672, some other useful names and star
catalogue numbers include: Alp or Alf CMi, 10 CMi, HR 2943,
Gl 280 A, Hip 37279, HD 61421, BD+05 1739, SAO 115756,
FK5 291, LHS 233, and ADS 6251 A.

According to one type of model calculations performed for the
NASA
Star and Exoplanet Database, the inner edge of Procyon A's
habitable zone is located relatively far from the star at
around 1.981 AUs from the star, while the outer edge lies even
farther out at around 4.003 AUs.
The distance from Procyon A where an Earth-type planet would be
"comfortable" with liquid water is centered around 3.0 AUs (about the
middle of the main asteriod belt in the Solar System between Mars and
Jupiter), where its orbit period would be 4.2 years long. If there is
life on any Earth-type planet orbiting Procyon A, it is likely to be
primitive single-cell bacteria under major bombardment by meteorites
and comets as Earth was for the first few billion years. If
oxygen-producing microbes have not yet had time to develop and generate
free oxygen in the atmosphere of such a planet, it probably would not
have an ozone layer (O3) although Procyon A
puts out more ultraviolet radiation than Sol. (For an illustrated discussion,
see Christoph Kulmann's web page on the potential
habitable
zone around Procyon A.)

This much dimmer star is a white dwarf (DQZ,A4 or QZ,A4 VII), whose
close proximity and large disparity in brightness with its primary
have made precise determination of its luminosity, colors, and
spectrum difficult
(Irwin
et al, 1992). At least 15,000 times fainter than Procyon A,
it is also only 6/10,000th as luminous as Sol. Procyon B appears
to have 60.2 percent of Sol's mass
(Girard
et al, 2000)
but only about two percent of its diameter. In fact, its diameter
may be no more than about 17,000 km (about 10,500 miles), which is
only about 30 percent more than Earth's. On the other hand, white
dwarfs are incredibly dense objects because they squeeze a stellar
mass into a planetary volume, and so Procyon B's average density is
estimated to be over two tons to the cubic inch.

While tiny compared to main sequence stars, white dwarf stars are
actually intensely hot, but without the internal heat of fusion to
keep them burning, they gradually cool, redden, and fade away. As
some star catalogues note that Star B actually appears yellowish,
it is likely that this "white" dwarf is been cooling for a very
long time and is much older than
Sirius B.
Useful star catalogue numbers for this Procyon B include Gl 280 B
and ADS 6251 B.

Hunt for Substellar Companions

A search for faint companions using the
Hubble Space Telescope
from 1995 to 1999 found no supporting evidence for a large Jupiter
or brown dwarf sized object, although the observed positions of
Procyon AB -- Gl 280 AB -- differed from published orbital
elements
(Schroeder
et al, 2000).

Closest Neighbors

The following star systems are located within 10
light-years of Procyon AB.

Try Professor Jim Kaler's
Stars
site for other information about
Procyon
at the University of Illinois' Department of Astronomy. For another
illustrated discussion, see Christoph Kulmann's web page on the potential
habitable
zone around Procyon A.

The name Procyon was used by the Ancient Greeks, which the Romans
translated into Latin equivalent as "Antecanis" or "Before the Dog"
because Procyon rises immediately before Sirius, the "Dog Star." For
more information about the stars and objects in this constellation, go
to Christine Kronberg's
Canis
Minor. For an illustration, see David Haworth's
Canis
Minor.

For more information about stars including spectral and luminosity
class codes, go to ChView's webpage on
The Stars of
the Milky Way.